U.S. patent number 7,494,943 [Application Number 11/543,880] was granted by the patent office on 2009-02-24 for method for using film formation apparatus.
This patent grant is currently assigned to Tokyo Electron Limited. Invention is credited to Takehiko Fujita, Norifumi Kimura, Naotaka Noro, Yamato Tonegawa.
United States Patent |
7,494,943 |
Noro , et al. |
February 24, 2009 |
Method for using film formation apparatus
Abstract
In a method for using a film formation apparatus for a
semiconductor process, process conditions of a film formation
process are determined. The process conditions include a preset
film thickness of a thin film to be formed on a target substrate.
Further, a timing of performing a cleaning process is determined in
accordance with the process conditions. The timing is defined by a
threshold concerning a cumulative film thickness of the thin film.
The cumulative film thickness does not exceed the threshold where
the film formation process is repeated N times (N is a positive
integer), but exceeds the threshold where the film formation
process is repeated N+1 times. The method includes continuously
performing first to Nth processes, each consisting of the film
formation process, and performing the cleaning process after the
Nth process and before an (N+1)th process consisting of the film
formation process.
Inventors: |
Noro; Naotaka (Nirasaki,
JP), Tonegawa; Yamato (Kai, JP), Fujita;
Takehiko (Kai, JP), Kimura; Norifumi (Kofu,
JP) |
Assignee: |
Tokyo Electron Limited (Tokyo,
JP)
|
Family
ID: |
37985929 |
Appl.
No.: |
11/543,880 |
Filed: |
October 6, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070093075 A1 |
Apr 26, 2007 |
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Foreign Application Priority Data
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Oct 20, 2005 [JP] |
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2005-305866 |
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Current U.S.
Class: |
438/30;
257/E21.227; 257/E21.218; 257/E21.311; 438/680; 438/778;
257/E21.319; 257/E21.17; 438/905 |
Current CPC
Class: |
C23C
16/52 (20130101); C23C 16/4405 (20130101); Y10S
438/905 (20130101) |
Current International
Class: |
H01L
21/00 (20060101) |
Field of
Search: |
;438/30,249,513,657,680,778,905 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Nhu; David
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Claims
What is claimed is:
1. A method for using a film formation apparatus for a
semiconductor process, the method comprising: applying process
conditions of a film formation process for forming a thin film on a
target substrate accommodated in a reaction chamber of the film
formation apparatus, the process conditions including a preset film
thickness of the thin film to be formed on the target substrate;
applying a timing of performing a cleaning process for removing a
by-product film deposited on an inner surface of the reaction
chamber due to the film formation process, in accordance with the
process conditions, the timing being defined by a threshold
concerning a cumulative film thickness that is a value obtained by
multiplying a number of repetitions of the film formation process
by the preset film thickness, wherein the cumulative film thickness
does not exceed the threshold where the film formation process is
repeated N times (N is a positive integer), but exceeds the
threshold where the film formation process is repeated N+1 times;
performing first to Nth processes, each consisting of the film
formation process, continuously without interposing the cleaning
process therebetween; and performing the cleaning process after the
Nth process and before an (N+1)th process consisting of the film
formation process.
2. The method for using a film formation apparatus according to
claim 1, wherein the film formation process is arranged to supply a
film formation gas into the reaction chamber, and set an interior
of the reaction chamber at a temperature and a pressure to
decompose the film formation gas, and the by-product film is
derived from the film formation gas.
3. The method for using a film formation apparatus according to
claim 2, wherein the film formation gas comprises diehiorosilane
and ammonia, the thin film comprises a silicon nitride film, and
the threshold is set at 0.7 .mu.m.
4. The method for using a film formation apparatus according to
claim 2, wherein the film formation gas comprises
hexaehlorodisilane and ammonia, the thin film comprises a silicon
nitride film, and the threshold is set at 1.5 .mu.m.
5. The method for using a film formation apparatus according to
claim 2, wherein the film formation gas comprises mono-silane, the
thin film comprises a poly-crystalline silicon film, and the
threshold is set at 6 .mu.m.
6. The method for using a film formation appartus according to
claim 1, wherein the cleaning process is arranged to supply a
cleaning gas into the reaction chamber, and set an interior of the
reaction chamber at a temperature and a pressure to cause the
cleaning gas to react with the by-product film.
7. The method for using a film formation apparatus according to
claim 6, wherein the thin film comprises a silicon-containing
film.
8. The method for using a film formation apparatus according to
claim 7, wherein the cleaning gas is a gas containing fluorine or
chlorine.
9. The method for using a film formation apparatus according to
claim 1, wherein the threshold is determined in accordance with a
relationship between a number of cracks generated on the by-product
film and the cumulative film thickness.
10. The method for using a film formation apparatus according to
claim 1, wherein the threshold is determined in accordance with a
relationship between a number of particles deposited on the thin
film and the cumulative film thickness.
11. A method for using a film formation apparatus for a
semiconductor process, the method comprising: applying process
conditions of a film formation process for forming a thin film on a
target substrate accommodated in a reaction chamber of the film
formation apparatus, the process conditions including a preset film
thickness of the thin film to be formed on the target substrate;
applying a timing of performing a cleaning process for removing a
by-product film deposited on an inner surface of the reaction
chamber due to the film formation process, in accordance with the
process conditions, the timing being defined by a threshold
concerning a cumulative film thickness that is a value obtained by
multiplying a number of repetitions of the film formation process
by the preset film thickness, wherein the cumulative film thickness
does not exceed the threshold where the film formation process is
repeated N times (N is a positive integer), but exceeds the
threshold where the film formation process is repeated N+1 times;
performing first to Nth processes, each consisting of the film
formation process, continuously without interposing the cleaning
process therebetween, while applying the process conditions to the
first to Nth processes; and performing the cleaning process by
applying the timing thereto after the Nth process and before an
(N+1)th process consisting of the film formation process.
12. The method for using a film formation apparatus according to
claim 11, wherein the film formation process is arranged to supply
a film formation gas into the reaction chamber, and set an interior
of the reaction chamber at a temperature and a pressure to
decompose the film formation gas, and the by-product film is
derived from the film formation gas.
13. The method for using a film formation apparatus according to
claim 12, wherein the film formation gas comprises dichlorosilane
and ammonia, the thin film comprises a silicon nitride film, and
the threshold is set at 0.7 .mu.m.
14. The method for using a film formation apparatus according to
claim 12, wherein the film formation gas comprises
hexachiorodisilane and ammonia, the thin film comprises a silicon
nitride film, and the threshold is set at 1.5 .mu.m.
15. The method for using a film formation apparatus according to
claim 12, wherein the film formation gas comprises mono-silane, the
thin film comprises a poly-crystalline silicon film, and the
threshold is set at 6 .mu.m.
16. The method for using a film formation apparatus according to
claim 11, wherein the cleaning process is arranged to supply a
cleaning gas into the reaction chamber, and set an interior of the
reaction chamber at a temperature and a pressure to cause the
cleaning gas to react with the by-product film.
17. The method for using a film formation apparatus according to
claim 16, wherein the thin film comprises a silicon-containing
film.
18. The method for using a film formation apparatus according to
claim 17, wherein the cleaning gas is a gas containing fluorine or
chlorine.
19. The method for using a film formation apparatus according to
claim 11, wherein the threshold is determined in accordance with a
relationship between a number of cracks generated on the by-product
film and the cumulative film thickness.
20. The method for using a film formation apparatus according to
claim 11, wherein the threshold is determined in accordance with a
relationship between a number of particles deposited on the thin
film and the cumulative film thickness.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority
from prior Japanese Patent Application No. 2005-305866, filed Oct.
20, 2005, the entire contents of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a film formation apparatus for a
semiconductor process for forming a film on a target substrate,
such as a semiconductor wafer, and also to a method for using the
apparatus. The term "semiconductor process" used herein includes
various kinds of processes which are performed to manufacture a
semiconductor device or a structure having wiring layers,
electrodes, and the like to be connected to a semiconductor device,
on a target substrate, such as a semiconductor wafer or a glass
substrate used for an LCD (Liquid Crystal Display) or FPD (Flat
Panel Display), by forming semiconductor layers, insulating layers,
and conductive layers in predetermined patterns on the target
substrate.
2. Description of the Related Art
In manufacturing semiconductor devices, a process, such as CVD
(Chemical Vapor Deposition), is performed to form a thin film, such
as a silicon nitride film, silicon oxide film, poly-crystalline
silicon film, on a target substrate, such as a semiconductor wafer.
For example, a film formation process of this kind is arranged to
form a thin film on a semiconductor wafer, as follows.
At first, the interior of the reaction tube (reaction chamber) of a
heat processing apparatus is heated by a heater at a predetermined
load temperature, and a wafer boat that holds a plurality of
semiconductor wafers is loaded. Then, the interior of the reaction
tube is heated up to a predetermined process temperature, and gas
inside the reaction tube is exhausted through an exhaust port, so
that the pressure inside the reaction tube is reduced to a
predetermined pressure.
Then, while the interior of the reaction tube is kept at the
predetermined temperature and pressure (kept exhausted), a film
formation gas is supplied through a process gas feed line into the
reaction tube. For example, in the case of CVD, when a film
formation gas is supplied into a reaction tube, the film formation
gas causes a thermal reaction and thereby produces reaction
products. The reaction products are deposited on the surface of
each semiconductor wafer, and form a thin film on the surface of
the semiconductor wafer.
Reaction products generated during the film formation process are
deposited (adhered) not only on the surface of the semiconductor
wafer, but also on, e.g., the inner surface of the reaction tube
and other members, the latter being as by-product films. If the
film formation process is continued while by-product films are
present on the interior of the reaction tube, some of the
by-product films separate therefrom and generate particles. These
particles may drop onto the semiconductor wafer, and reduce the
yield of semiconductor devices to be fabricated.
In order to solve this problem, cleaning of the interior of the
reaction tube is performed after the film formation process is
repeated several times. In this cleaning, the interior of the
reaction tube is heated at a predetermined temperature by a heater,
and a cleaning gas, such as a mixture gas of fluorine and a
halogen-containing acidic gas, is supplied into the reaction tube.
The by-product films deposited on the inner surface of the reaction
tube are dry-etched and removed by the cleaning gas. Jpn. Pat.
Appln. KOKAI Publication No. 3-293726 discloses a cleaning method
of this kind.
In order to suppress particle generation, it is preferable to
perform a cleaning process frequently, for example, to clean the
interior of a reaction tube every time a thin film is formed on a
semiconductor wafer. However, in this case, the downtime of the
heat processing apparatus becomes longer, thereby lowering the
productivity. Accordingly, it is required to suppress particle
generation, while improving the productivity. Further, as described
later, the present inventors have found that, when a film formation
process is performed after the interior of a reaction tube is
subjected to cleaning, a problem may arise in that the film
formation rate (deposition rate) is lowered, so the reproducibility
of the process is deteriorated.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a film formation
apparatus for a semiconductor process and a method for using the
same, which can suppress particle generation, while improving the
reproducibility and productivity of the process.
According to a first aspect of the present invention, there is
provided a method for using a film formation apparatus for a
semiconductor process, the method comprising:
determining process conditions of a film formation process for
forming a thin film on a target substrate accommodated in a
reaction chamber of the film formation apparatus, the process
conditions including a preset film thickness of the thin film to be
formed on the target substrate;
determining a timing of performing a cleaning process for removing
a by-product film deposited on an inner surface of the reaction
chamber due to the film formation process, in accordance with the
process conditions, the timing being defined by a threshold
concerning a cumulative film thickness that is a value obtained by
multiplying the number of repetitions of the film formation process
by the preset film thickness, wherein the cumulative film thickness
does not exceed the threshold where the film formation process is
repeated N times (N is a positive integer), but exceeds the
threshold where the film formation process is repeated N+1
times;
performing first to Nth processes, each consisting of the film
formation process, continuously without interposing the cleaning
process therebetween; and
performing the cleaning process after the Nth process and before an
(N+1)th process consisting of the film formation process.
According to a second aspect of the present invention, there is
provided a film formation apparatus for a semiconductor process,
comprising:
a reaction chamber configured to accommodate a target
substrate;
an exhaust system configured to exhaust an interior of the reaction
chamber;
a film formation gas supply circuit configured to supply a film
formation gas into the reaction chamber, the film formation gas
being used for performing a film formation process;
a cleaning gas supply circuit configured to supply a cleaning gas
into the reaction chamber, the cleaning gas being used for
performing a cleaning process to remove a by-product film deposited
on an inner surface of the reaction chamber due to the film
formation process; and
a control section configured to control an operation of the
apparatus,
wherein the control section executes
recognizing process conditions of the film formation process, the
process conditions including a preset film thickness of the thin
film to be formed on the target substrate;
determining a timing of performing the cleaning process in
accordance with the process conditions, the timing being defined by
a threshold concerning a cumulative film thickness that is a value
obtained by multiplying the number of repetitions of the film
formation process by the preset film thickness, wherein the
cumulative film thickness does not exceed the threshold where the
film formation process is repeated N times (N is a positive
integer), but exceeds the threshold where the film formation
process is repeated N+1 times;
performing first to Nth processes, each consisting of the film
formation process, continuously without interposing the cleaning
process therebetween; and
performing the cleaning process after the Nth process and before an
(N+1)th process consisting of the film formation process.
According to a third aspect of the present invention, there is
provided a computer readable medium containing program instructions
for execution on a processor, which, when executed by the
processor, cause a film formation apparatus for a semiconductor
process to execute
recognizing process conditions of a film formation process for
forming a thin film on a target substrate accommodated in a
reaction chamber of the film formation apparatus, the process
conditions including a preset film thickness of the thin film to be
formed on the target substrate;
determining a timing of performing a cleaning process for removing
a by-product film deposited on an inner surface of the reaction
chamber due to the film formation process, in accordance with the
process conditions, the timing being defined by a threshold
concerning a cumulative film thickness that is a value obtained by
multiplying the number of repetitions of the film formation process
by the preset film thickness, wherein the cumulative film thickness
does not exceed the threshold where the film formation process is
repeated N times (N is a positive integer), but exceeds the
threshold where the film formation process is repeated N+1
times;
performing first to Nth processes, each consisting of the film
formation process, continuously without interposing the cleaning
process therebetween; and
performing the cleaning process after the Nth process and before an
(N+1)th process consisting of the film formation process.
Additional objects and advantages of the invention will be set
forth in the description which follows, and in part will be obvious
from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
The accompanying drawings, which are incorporated in and constitute
a part of the specification, illustrate embodiments of the
invention, and together with the general description given above
and the detailed description of the embodiments given below, serve
to explain the principles of the invention.
FIG. 1 is a view showing a vertical heat processing apparatus
according to an embodiment of the present invention;
FIG. 2 is a view showing the structure of the control section of
the apparatus shown in FIG. 1;
FIG. 3 is a view showing the recipe of a film formation process and
a cleaning process according to an embodiment of the present
invention;
FIG. 4 is a graph showing the relationship between the cumulative
film thickness on target substrates and the number of cracks on a
by-product film, where a film formation process using DCS and
ammonia to form a silicon nitride film having a thickness of 0.1
.mu.m was repeated a plurality of times;
FIG. 5 is a graph showing the relationship between the cumulative
film thickness on target substrates and the number of cracks on a
by-product film, where a film formation process using DCS and
ammonia to form a silicon nitride film having a thickness of 0.2
.mu.m was repeated a plurality of times;
FIG. 6 is a graph showing the number of particles deposited on a
silicon nitride film formed by each film formation process.
FIG. 7 is a graph showing the relationship between the cumulative
film thickness on target substrates and the number of cracks on a
by-product film, where a film formation process using DCS and
ammonia to form a silicon nitride film having a thickness of 0.1
.mu.m was repeated a plurality of times, under conditions different
from those for FIG. 4;
FIG. 8 is a graph showing the relationship between the cumulative
film thickness on target substrates and the number of cracks on a
by-product film, where a film formation process using HCD and
ammonia to form a silicon nitride film having a thickness of 0.1
.mu.m was repeated a plurality of times; and
FIG. 9 is a graph showing the relationship between the cumulative
film thickness on target substrates and the number of cracks on a
by-product film, where a film formation process using mono-silane
to form a poly-crystalline silicon film having a thickness of 0.5
.mu.m was repeated a plurality of times.
DETAILED DESCRIPTION OF THE INVENTION
In the process of developing the present invention, the inventors
studied the decrease in deposition rate and particle contamination
after cleaning with regard to conventional methods for cleaning the
interior of a reaction tube used in a film formation apparatus for
a semiconductor process. As a result, the inventors have arrived at
the findings given below.
Specifically, after a film formation process is repeated a
plurality of times, the inner surface of a reaction tube may be
damaged and suffer cracks formed thereon due to stress generated by
by-product films. Particularly, where a film formation process of a
silicon nitride film is performed in a quartz reaction tube,
by-product films formed by this process apply a relatively large
stress on the reaction tube. Consequently, large cracks tend to be
easily formed on the inner surface of the reaction tube.
The cracks are exposed on the inner surface of the reaction tube
when the by-product films are removed therefrom by cleaning. The
cracks on the inner surface of the reaction tube increase the
surface area, and may thereby cause the deposition rate to
decrease. Further, quartz powder can easily separate and drop from
the cracks of the reaction tube and generate particles.
The crack generation on the inner surface of a quartz reaction tube
is highly correlated with the crack generation on by-product films
formed thereon, such that the number of cracks on the inner surface
of the reaction tube is small, as long as the number of cracks on
the by-product films is small. Accordingly, where a cleaning
process is performed for the interior of the reaction tube before
cracks on the by-product films increase, it is possible to prevent
the problems described above due to cracks on the inner surface of
the reaction tube.
Embodiments of the present invention achieved on the basis of the
findings given above will now be described with reference to the
accompanying drawings. In the following description, the
constituent elements having substantially the same function and
arrangement are denoted by the same reference numerals, and a
repetitive description will be made only when necessary.
FIG. 1 is a view showing a vertical heat processing apparatus
according to an embodiment of the present invention. As shown in
FIG. 1, the heat processing apparatus 1 includes an essentially
cylindrical reaction tube (reaction chamber) 2 whose longitudinal
direction is set in the vertical direction. The reaction tube 2 is
made of a heat-resistant and corrosion-resistant material, such as
quartz.
The top of the reaction tube 2 is formed as an essentially conical
ceiling 3 whose diameter decreases toward the top. The ceiling 3
has an exhaust port 4 formed at the center, for exhausting gas
inside the reaction tube 2. The exhaust port 4 is connected to an
exhaust section GE through an airtight exhaust line 5. The exhaust
section GE has a pressure adjusting mechanism including, e.g., a
valve and a vacuum exhaust pump. The exhaust section GE is used to
exhaust the atmosphere within the reaction tube 2, and set it at a
predetermined pressure (vacuum level).
A lid 6 is disposed below the reaction tube 2. The lid 6 is made of
a heat-resistant and corrosion-resistant material, such as quartz.
The lid 6 is moved up and down by a boat elevator described later
(not shown in FIG. 1, but shown in FIG. 2 with a reference symbol
128). When the lid 6 is moved up by the boat elevator, the bottom
of the reaction tube 2 (load port) is closed. When the lid 6 is
moved down by the boat elevator, the bottom of the reaction tube 2
(load port) is opened.
A thermally insulating cylinder 7 is disposed on the lid 6. The
thermally insulating cylinder 7 is provided with a planar heater 8
made of a resistive heating body to prevent the temperature inside
the reaction tube from decreasing due to heat radiation from the
load port of the reaction tube 2. The heater 8 is supported at a
predetermined height level relative to the top face of the lid 6 by
a cylindrical support 9.
A rotary table 10 is disposed above the thermally insulating
cylinder 7. The rotary table 10 is used as a table for rotatably
mounting thereon a wafer boat 11 that holds target substrates, such
as semiconductor wafers W. Specifically, the rotary table 10 is
connected to a rotary shaft 12 disposed therebelow. The rotary
shaft 12 passes through the center of the heater 8 and is connected
to a rotation mechanism 13 for rotating the rotary table 10.
The rotation mechanism 13 is mainly formed of a motor (not shown),
and a rotation feeder 15 with an axle 14 that airtightly penetrates
the lid 6 from below. The axle 14 is coupled to the rotary shaft 12
of the rotary table 10, to transmit the rotational force of the
motor to the rotary table 10 through the rotary shaft 12. When the
axle 14 is rotated by the motor of the rotation mechanism 13, the
rotational force of the axle 14 is transmitted to the rotary shaft
12, and the rotary table 10 is rotated.
The wafer boat 11 is configured to hold a plurality of, e.g., 100,
semiconductor wafers W at predetermined intervals in the vertical
direction. The wafer boat 11 is made of a heat-resistant and
corrosion-resistant material, such as quartz. Since the wafer boat
11 is mounted on the rotary table 10, the wafer boat 11 is rotated
along with the rotary table 10, and thus the semiconductor wafers W
held in the wafer boat 11 are rotated.
A heater 16 made of, e.g., a resistive heating body is disposed
near the reaction tube 2 to surround the tube 2. The interior of
the reaction tube 2 is heated by the heater 16, so that the
semiconductor wafers W are heated up (increase in temperature) to a
predetermined temperature.
Process gas feed lines 17 penetrate the sidewall of the reaction
tube 2 near the bottom, and are used for supplying process gases
(such as a film formation gas and a cleaning gas) into the reaction
tube 2. Each process gas feed line 17 is connected to a process gas
supply source GS1 through a mass-flow controller (MFC) described
later (not shown in FIG. 1, but shown in FIG. 2 with a reference
symbol 125).
For example, as a film formation gas to form a silicon nitride film
on the semiconductor wafers W, a mixture gas of dichlorosilane
(DCS: SiH.sub.2Cl.sub.2) and ammonia (NH.sub.3) is used.
Alternatively, as a film formation gas to form a silicon nitride
film on the semiconductor wafers W, a mixture gas of
hexachlorodisilane (HCD: Si.sub.2Cl.sub.6) and ammonia (NH.sub.3)
may be used. Alternatively, for example, as a film formation gas to
form a poly-crystalline silicon film on the semiconductor wafers W,
mono-silane (SiH.sub.4) may be used. For example, as a cleaning gas
to remove by-product films deposited inside the reaction tube 2, a
gas containing fluorine or chlorine is used. Specifically, a
mixture gas of fluorine (F.sub.2), hydrogen fluoride (HF), and
nitrogen (N.sub.2) is used as a cleaning gas.
Although FIG. 1 shows only one process gas feed line 17, a
plurality of process gas feed lines 17 are disposed in accordance
with gases to be supplied into the reaction tube 2 in the
respective process steps, in this embodiment. Specifically, a film
formation gas feed line for supplying the film formation gas into
the reaction tube 2 and a cleaning gas feed line for supplying the
cleaning gas into the reaction tube 2 penetrate the sidewall of the
reaction tube 2 near the bottom.
A purge gas feed line 18 also penetrates the sidewall of the
reaction tube 2 near the bottom. The purge gas feed line 18 is
connected to a purge gas supply source GS2 through an MFC described
later (not shown in FIG. 1, but shown in FIG. 2 with a reference
symbol 125).
The heat processing apparatus 1 further includes a control section
100 for controlling respective portions of the apparatus. FIG. 2 is
a view showing the structure of the control section 100. As shown
in FIG. 2, the control section 100 is connected to an operation
panel 121, (a group of) temperature sensors 122, (a group of)
pressure gages 123, a heater controller 124, MFCs 125, valve
controllers 126, a vacuum pump 127, a boat elevator 128, and so
forth.
The operation panel 121 includes a display screen and operation
buttons, and is configured to transmit operator's instructions to
the control section 100, and show various data transmitted from the
control section 100 on the display screen. Temperature sensors 122
are configured to measure the temperature at respective portions
inside the reaction tube 2 and exhaust line 5, and transmit
measurement values to the control section 100. The pressure gages
123 are configured to measure the pressure at respective portions
inside the reaction tube 2 and exhaust line 5, and transmit
measurement values to the control section 100.
The heater controller 124 is configured to control the heaters 8
and 16. The heater controller 124 turns on the heaters 8 and 16 to
generate heat, in accordance with instructions from the control
section 100. The heater controller 124 is also configured to
measure the power consumption of the heaters 8 and 16, and transmit
it to the control section 100.
The MFCs 125 are respectively disposed on piping lines, such as the
process gas feed lines 17 and purge gas feed line 18. Each MFC 125
is configured to control the flow rate of a gas flowing through the
corresponding line in accordance with instructed values received
from the control section 100. Further, each MFC 125 is configured
to measure the flow rate of a gas actually flowing, and transmit
the reading to the control section 100.
The valve controllers 126 are respectively disposed on piping lines
and configured to control the opening rate of valves disposed on
piping lines, in accordance with instructed values received from
the control section 100. The vacuum pump 127 is connected to the
exhaust line 5 and configured to exhaust gas inside the reaction
tube 2.
The boat elevator 128 is configured to move up the lid 6, so as to
load the wafer boat 11 (semiconductor wafers W) placed on the
rotary table 10 into the reaction tube 2. The boat elevator 128 is
also configured to move the lid 6 down, so as to unload the wafer
boat 11 (semiconductor wafers W) placed on the rotary table 10 from
the reaction tube 2.
The control section 100 includes a recipe storage portion 111, a
ROM 112, a RAM 113, an I/O port 114, and a CPU 115. These members
are inter-connected via a bus 116 so that data can be transmitted
between them through the bus 116.
The recipe storage portion 111 stores a setup recipe and a
plurality of process recipes. After the heat processing apparatus 1
is manufactured, only the setup recipe is initially stored. The
setup recipe is executed when a thermal model or the like for a
specific heat processing apparatus is formed. The process recipes
are prepared respectively for heat processes to be actually
performed by a user. Each process recipe prescribes temperature
changes at respective portions, pressure changes inside the
reaction tube 2, start/stop timing for supply of process gases, and
supply rates of process gases, from the time semiconductor wafers W
are loaded into the reaction tube 2 to the time processed wafers W
are unloaded.
The ROM 112 is a recording medium formed of an EEPROM, flash
memory, or hard disc, and is used to store operation programs
executed by the CPU 115 or the like. The RAM 113 is used as a work
area for the CPU 115.
The I/O port 114 is connected to the operation panel 121,
temperature sensors 122, pressure gages 123, heater controller 124,
MFCs 125, valve controllers 126, vacuum pump 127, and boat elevator
128, and is configured to control output/input of data or
signals.
The CPU (Central Processing Unit) 115 is the hub of the control
section 100. The CPU 115 is configured to run control programs
stored in the ROM 112, and control an operation of the heat
processing apparatus 1, in accordance with a recipe (process
recipe) stored in the recipe storage portion 111, following
instructions from the operation panel 121. Specifically, the CPU
115 causes the temperature sensors 122, pressure gages 123, and
MFCs 125 to measure temperatures, pressures, and flow rates at
respective portions inside the reaction tube 2 and exhaust line 5.
Further, the CPU 115 outputs control signals, based on measurement
data, to the heater controller 124, MFCs 125, valve controllers
126, and vacuum pump 127, to control the respective portions
mentioned above in accordance with a process recipe.
In each of the process recipes, process conditions are prescribed
for a film formation process and a cleaning process. The film
formation process is a process for forming a thin film on
semiconductor wafers W, wherein the process comprises a series of
steps of loading the semiconductor wafers W into the heat
processing apparatus 1, forming the thin film on the semiconductor
wafers W, and unloading the semiconductor wafers W with the thin
film formed thereon, as described later. The cleaning process is a
process for cleaning the interior of the heat processing apparatus
1.
For example, the conditions of a process recipe are prescribed such
that a film formation process is repeated a plurality of times, and
then a cleaning process is performed, as shown in FIG. 3. According
to an embodiment of the present invention, a cleaning process is
performed in a state where the cumulative film thickness of thin
films, formed on target substrates by repetition of a film
formation process, is less than a predetermined value (threshold),
i.e., before the cumulative film thickness exceeds the
threshold.
The cumulative film thickness means the total film thickness of
thin films formed by repeating a film formation process a plurality
of times after the cleaning process. For example, where a film
formation process for forming a thin film having a thickness of 0.2
.mu.m on semiconductor wafers W is executed twice, the cumulative
film thickness is expressed by 0.2.times.2=0.4 .mu.m.
The threshold denotes a preset value in accordance with the type of
a thin film formed on target substrates, the type of film formation
gases, and so forth. If the heat processing apparatus with a
condition exceeding the threshold is used to form a thin film on
target substrates, by-product films deposited inside the apparatus
tend to be cracked (form cracks), and thereby generate
particles.
According to a process recipe thus prepared, a cleaning process is
performed before the cumulative film thickness of thin films,
formed on target substrates by repetition of a film formation
process, exceeds the threshold. Consequently, by-product films
deposited inside a heat processing apparatus are prevented from
being cracked, thereby suppressing particle generation. Further,
the film formation process is repeated a plurality of times before
one cleaning process, so the productivity is improved. In other
words, the productivity can be improved while the particle
generation is suppressed.
Next, an explanation will be given of a method for using the heat
processing apparatus 1 described above, with reference to FIG. 3.
In summary, at first, a silicon nitride film is formed on
semiconductor wafers W within the reaction tube 2. Then, by-product
films, which contain silicon nitride as the main component (i.e.,
at 50% or more), deposited inside the reaction tube 2 are removed.
FIG. 3 is a view showing the recipe of a film formation process and
a cleaning process according to an embodiment of the present
invention.
The respective components of the heat processing apparatus 1
described below are operated under the control of the control
section 100 (CPU 115). The temperature and pressure inside the
reaction tube 2 and the gas flow rates during the processes are set
in accordance with the recipe shown in FIG. 3, while the control
section 100 (CPU 115) controls the heater controller 124 (for the
heaters 8 and 16), MFCs 125 (on the process gas feed line 17 and
purge gas feed line 18), valve controllers 126, and vacuum pump
127, as described above.
In the first film formation process (Film formation process FP1),
at first, the interior of the reaction tube 2 is heated by the
heater 16 at a predetermined load temperature, such as 300.degree.
C., as shown in FIG. 3, (a). Further, nitrogen (N.sub.2) is
supplied through the purge gas feed line 18 into the reaction tube
2 at a predetermined flow rate, as shown in FIG. 3, (c). Then, a
wafer boat 11 that holds semiconductor wafers W is placed on the
lid 6, and the lid 6 is moved up by the boat elevator 128.
Consequently, the wafer boat 11 with the semiconductor wafers W
supported thereon is loaded into the reaction tube 2 and the
reaction tube 2 is airtightly closed (load step).
Then, nitrogen is supplied through the purge gas feed line 18 into
the reaction tube 2 at a predetermined flow rate, as shown in FIG.
3, (c). Further, the interior of the reaction tube 2 is heated by
the heater 16 to a predetermined film formation temperature
(process temperature), such as 800.degree. C., as shown in FIG. 3,
(a). Furthermore, gas inside the reaction tube 2 is exhausted to
set the interior of the reaction tube 2 at a predetermined
pressure, such as 40 Pa (0.3 Torr), as shown in FIG. 3, (b). The
pressure reduction and heating operations are kept performed until
the reaction tube 2 is stabilized at the predetermined pressure and
temperature (stabilization step).
The motor of the rotation mechanism 13 is controlled to rotate the
wafer boat 11 through the rotary table 10. The wafer boat 11 is
rotated along with the semiconductor wafers W supported thereon,
thereby uniformly heating the semiconductor wafers W.
When the interior of the reaction tube 2 is stabilized at the
predetermined pressure and temperature, the supply of nitrogen
through the purge gas feed line 18 is stopped. Then, a first film
formation gas containing silicon and a second film formation gas
containing nitrogen are supplied through the process gas feed line
17 into the reaction tube 2. In this embodiment, the first film
formation gas contains DCS supplied at a predetermined flow rate,
such as 0.2 liters/min, as shown in FIG. 3, (d). The second film
formation gas contains ammonia (NH.sub.3) supplied at a
predetermined flow rate, such as 2 liters/min, as shown in FIG. 3,
(e).
The DCS and ammonia supplied into the reaction tube 2 cause a
thermal decomposition reaction, using heat inside the reaction tube
2. The decomposition components produce silicon nitride
(Si.sub.3N.sub.4), from which a silicon nitride film is formed on
the surface of the semiconductor wafers W (film formation
step).
When the silicon nitride film formed on the surface of the
semiconductor wafers W reaches a predetermined thickness of, e.g.,
0.2 .mu.m, the supply of DCS and ammonia through the process gas
feed line 17 is stopped. Then, the interior of the reaction tube 2
is exhausted, and nitrogen is supplied through the purge gas feed
line 18 at a predetermined flow rate, as shown in FIG. 3, (c). By
doing so, the gas inside the reaction tube 2 is exhausted to the
exhaust line 5 (purge step). It is preferable to perform cyclic
purging by repeating the gas exhaust and nitrogen gas supply for
the interior of the process tube 2 a plurality of times, in order
to reliably exhaust the gas inside the process tube 2.
Then, the interior of the reaction tube 2 is set by the heater 16
at a predetermined temperature, such as 300.degree. C., as shown in
FIG. 3, (a). Further, nitrogen is supplied through the purge gas
feed line 18 into the reaction tube 2 at a predetermined flow rate,
as shown in FIG. 3, (c). The pressure inside the process tube 2 is
thereby returned to atmospheric pressure, as shown in FIG. 3, (b).
Then, the lid 6 is moved down by the boat elevator 128, and the
wafer boat 11 is thereby unloaded (unload step). Consequently, the
first film formation process (film formation process FP1) is
completed.
Then, the second film formation process (film formation process
FP2) is executed, following the same procedure used in the film
formation process FP1. Specifically, the wafer boat 11 that holds
new semiconductor wafers W to form a silicon nitride film thereon
is loaded into the reaction tube 2 (load step). Then, the
stabilization step, film formation step, purge step, and unload
step are performed, under the same conditions used in the film
formation process FP1. Consequently, a silicon nitride film having
a predetermined thickness of, e.g., 0.2 .mu.m, is formed on the
surface of the new semiconductor wafers W loaded in the heat
processing apparatus 1.
Then, the third film formation process (film formation process FP3)
is executed, following the same procedure used in the film
formation process FP1. Specifically, the wafer boat 11 that holds
new semiconductor wafers W to form a silicon nitride film thereon
is loaded into the reaction tube 2 (load step). Then, the
stabilization step, film formation step, purge step, and unload
step are performed, under the same conditions used in the film
formation process FP1. Consequently, a silicon nitride film having
a predetermined thickness of, e.g., 0.2 .mu.m, is formed on the
surface of the new semiconductor wafers W loaded in the heat
processing apparatus 1.
Repeating this film formation process a plurality of times, silicon
nitride produced by the film formation process is deposited
(adhered) not only on the surface of semiconductor wafers W, but
also on the inner surface of the reaction tube 2 and so forth, as
by-product films. Accordingly, after the film formation process is
repeated a plurality of times, a cleaning process is performed for
the heat processing apparatus 1. As shown in FIG. 3, under the
conditions used in this film formation process, the cleaning
process is performed after the film formation process is executed
three times. This is so, because, if the film formation process is
executed one more time without interposing the cleaning process
(the fourth film formation process is performed), the cumulative
film thickness of silicon nitride films formed on semiconductor
wafers W reaches a value expressed by 0.2 .mu.m.times.4=0.8 .mu.m.
As described later, in light of the conditions used in this film
formation process, the threshold of the cumulative film thickness
is set at 0.7 .mu.m. Where the cumulative film thickness exceeds
the threshold, by-product films deposited inside the reaction tube
2 tend to be cracked much more, and thereby generate particles.
In the cleaning process, at first, the interior of the reaction
tube 2 is maintained by the heater 16 at a predetermined load
temperature, such as 300.degree. C., as shown in FIG. 3, (a).
Further, nitrogen is supplied through the purge gas feed line 18
into the reaction tube 2 at a predetermined flow rate, as shown in
FIG. 3, (c). Then, an empty wafer boat 11 that holds no
semiconductor wafers W is placed on the lid 6, and the lid 6 is
moved up by the boat elevator 128. Consequently, the wafer boat 11
is loaded into the reaction tube 2 and the reaction tube 2 is
airtightly closed (load step).
Then, nitrogen is supplied through the purge gas feed line 18 into
the reaction tube 2 at a predetermined flow rate, as shown in FIG.
3, (c). Further, the interior of the reaction tube 2 is heated by
the heater 16 at a predetermined cleaning temperature, such as
300.degree. C., as shown in FIG. 3, (a) Furthermore, gas inside the
reaction tube 2 is exhausted to set the interior of the reaction
tube 2 at a predetermined pressure, such as 53,200 Pa (400 Torr),
as shown in FIG. 3, (b). The pressure reduction and heating
operations are kept performed until the reaction tube 2 is
stabilized at the predetermined pressure and temperature
(stabilization step).
When the interior of the reaction tube 2 is stabilized at the
predetermined pressure and temperature, the supply of nitrogen
through the purge gas feed line 18 is stopped. Then, a cleaning gas
is supplied through the process gas feed line 17 into the reaction
tube 2. In this embodiment, the cleaning gas contains fluorine
(F.sub.2) supplied at a predetermined flow rate, such as 2
liters/min, as shown in FIG. 3(f), hydrogen fluoride (HF) supplied
at a predetermined flow rate, such as 0.2 liters/min, as shown in
FIG. 3, (g), and nitrogen or dilution gas supplied at a
predetermined flow rate, such as 8 liters/min, as shown in FIG. 3,
(c).
The cleaning gas is heated in the reaction tube 2, and fluorine in
the cleaning gas is activated, thereby forming a state in which a
number of reactive free atoms are present. The activated fluorine
comes into contact with by-product films (containing silicon
nitride as the main component) deposited on the inner surface of
the reaction tube 2 and so forth. Consequently, the by-product
films are etched and removed (cleaning step). In this cleaning
step, the temperature inside the reaction tube 2 is preferably
maintained at a temperature within a range of from 200.degree. C.
to 500.degree. C. Further, the pressure inside the reaction tube 2
is preferably maintained at a pressure within a range of from 13.3
Pa (0.1 Torr) to 53,320 Pa (400 Torr).
When the by-product films deposited inside the reaction tube 2 are
removed, the supply of the cleaning gas through the process gas
feed line 17 is stopped. Then, the interior of the reaction tube 2
is exhausted, and nitrogen is supplied through the purge gas feed
line 18 into the reaction tube 2 at a predetermined flow rate, as
shown in FIG. 3, (c). By doing so, the gas inside the reaction tube
2 is exhausted to the exhaust line 5 (purge step). It is preferable
to perform cyclic purging by repeating the gas exhaust and nitrogen
gas supply for the interior of the process tube 2 a plurality of
times, in order to reliably exhaust the gas inside the process tube
2.
Then, the interior of the reaction tube 2 is set by the heater 16
at a predetermined temperature, such as 300.degree. C., as shown in
FIG. 3, (a). Further, nitrogen is supplied through the purge gas
supply line 18 into the reaction tube 2 at a predetermined flow
rate, as shown in FIG. 3, (c). The pressure inside the process tube
2 is thereby returned to atmospheric pressure, as shown in FIG. 3,
(b). Then, the lid 6 is moved down by the boat elevator 128, and
the wafer boat 11 is thereby unloaded (unload step). Consequently,
the cleaning process is completed.
As the process described above is being performed, by-product films
deposited on the inner surface of the reaction tube 2, the surface
of the wafer boat 11, and so forth are removed. Thereafter, a wafer
boat 11 with a new lot of semiconductor wafers W mounted thereon is
placed on the lid 6, and the film formation process is started
again in the manner described above.
As described above, according to this embodiment, the cleaning
process is performed before the cumulative film thickness of
silicon nitride films, formed on semiconductor wafers W by
repetition of the film formation process, exceeds the threshold
(0.7 .mu.m, as described later). Consequently, by-product films
deposited inside the heat processing apparatus are prevented from
being cracked, thereby suppressing particle generation. Further,
the film formation process is repeated three times before one
cleaning process, so the productivity is improved. In other words,
the productivity can be improved while the particle generation is
suppressed.
EXPERIMENT 1
In order to define the timing for performing a cleaning process,
based on the threshold of the cumulative film thickness, for a film
formation process using DCS and ammonia to form a silicon nitride
film, a process was performed under the following conditions.
Specifically, while the interior of the reaction tube 2 was set at
800.degree. C. and 40 Pa (0.3 Torr), DCS set at 0.2 liters/min and
ammonia set at 2 liters/min were supplied, to form a silicon
nitride film on semiconductor wafers W. In this film formation
process, a quartz chip having a predetermined size was placed in
the reaction tube 2 to facilitate sampling of a by-product film.
After each film formation process, visual examination was performed
on the surface of the quartz chip with a by-product film deposited
thereon (and having a cumulative film thickness) to measure the
number of cracks. Specifically, one diagonal line was drawn on the
image of the quartz chip including the by-product film, and the
number of intersections of the diagonal line with lines (grooves)
formed by cracks were counted to quantify the cracks.
FIG. 4 is a graph showing the relationship between the cumulative
film thickness on target substrates and the number of cracks on a
by-product film, where a film formation process using the
conditions of Experiment 1 to form a silicon nitride film having a
thickness of 0.1 .mu.m was repeated a plurality of times. FIG. 5 is
a graph showing the relationship between the cumulative film
thickness on target substrates and the number of cracks on a
by-product film, where a film formation process using the
conditions of Experiment 1 to form a silicon nitride film having a
thickness of 0.2 .mu.m was repeated a plurality of times.
As shown in FIGS. 4 and 5, where the cumulative film thickness was
0.7 .mu.m or less, cracks were scarcely generated. On the other
hand, where the cumulative film thickness exceeded 0.7 .mu.m, a lot
of cracks were generated. From these results, it has been found
that the threshold of the cumulative film thickness should be set
at 0.7 .mu.m, regardless of the preset film thickness of a silicon
nitride film formed by one film formation process.
As described above, where DCS and ammonia are used to form a
silicon nitride film, the threshold of the cumulative film
thickness is set at 0.7 .mu.m. For example, where a silicon nitride
film of 0.2 .mu.m is formed on a semiconductor wafer W, as
described above, a cleaning process is performed after the film
formation process is repeated three times. Alternatively, where a
silicon nitride film of 0.1 .mu.m is formed on a semiconductor
wafer W, a cleaning process is performed after the film formation
process is repeated seven times. Accordingly, each process recipe
is prepared in accordance with a set of process conditions.
EXPERIMENT 2
In relation to the method according to the embodiment described
above, silicon nitride films formed by the first to third film
formation processes FP1 to FP3 were examined in terms of the number
of particles deposited thereon. At this time, the number of
particles was confirmed for semiconductor wafers W placed at the
top (TOP) and bottom (BTM) of the wafer boat 11. Further, for
comparison, a silicon nitride film formed by a fourth film
formation process FP4 was also examined in terms of the number of
particles deposited thereon. The fourth film formation process FP4
was performed after the third film formation process FP3, without
interposing a cleaning process therebetween. FIG. 6 is a graph
showing the number of particles deposited on a silicon nitride film
formed by each film formation process.
As shown in FIG. 6, the number of particles on the silicon nitride
film formed by each of the film formation processes FP1 to FP3 was
very small. On the other hand, the number of particles on the
silicon nitride film formed by the film formation process FP4 was
very large. From these results, it has been confirmed that particle
generation within the heat processing apparatus 1 is suppressed by
performing a cleaning process before the cumulative film thickness
exceeds 0.7 .mu.m (threshold).
EXPERIMENT 3
In order to confirm the dependency of the threshold of the
cumulative film thickness relative to the process temperature,
process pressure, and process gas flow rate, for a film formation
process using DCS and ammonia to form a silicon nitride film, a
process was performed under the following conditions. Specifically,
while the interior of the reaction tube 2 was set at 600.degree. C.
and 133 Pa (1 Torr), DCS set at 0.1 liters/min and ammonia set at
0.5 liters/min were supplied, to form a silicon nitride film on
semiconductor wafers W.
FIG. 7 is a graph showing the relationship between the cumulative
film thickness on target substrates and the number of cracks on a
by-product film, where a film formation process using the
conditions of Experiment 3 to form a silicon nitride film having a
thickness of 0.1 .mu.m was repeated a plurality of times. As shown
in FIG. 7, also in this case, where the cumulative film thickness
was 0.7 .mu.m or less, cracks were scarcely generated, although
conditions different from the former case were used in terms of
process temperature, process pressure, and process gas flow rate.
On the other hand, where the cumulative film thickness exceeded 0.7
.mu.m, a lot of cracks were generated. From these results, it has
been found that, where DCS and ammonia are used to form a silicon
nitride film, the threshold of the cumulative film thickness should
be set at 0.7 .mu.m, regardless of the preset process temperature,
process pressure, and process gas flow rate.
EXPERIMENT 4
In order to find the threshold of the cumulative film thickness,
for a film formation process using a different film formation gas,
a process was performed under the following conditions. In
Experiment 4, the film formation process employed
hexachlorodisilane (HCD) and ammonia to form a silicon nitride
film. Specifically, while the interior of the reaction tube 2 was
set at 600.degree. C. and 40 Pa (0.3 Torr), HCD set at 0.01
liters/min and ammonia set at 2 liters/min were supplied, to form a
silicon nitride film on semiconductor wafers W.
FIG. 8 is a graph showing the relationship between the cumulative
film thickness on target substrates and the number of cracks on a
by-product film, where a film formation process using the
conditions of Experiment 4 to form a silicon nitride film having a
thickness of 0.1 .mu.m was repeated a plurality of times. As shown
in FIG. 8, where the cumulative film thickness was 1.5 .mu.m or
less, cracks were scarcely generated. On the other hand, where the
cumulative film thickness exceeded 1.5 .mu.m, a lot of cracks were
generated. From these results, it has been found that, where HCD
and ammonia are used to form a silicon nitride film, the threshold
of the cumulative film thickness should be set at 1.5 .mu.m.
EXPERIMENT 5
In order to find the threshold of the cumulative film thickness,
for a film formation process using a further different film
formation gas, a process was performed under the following
conditions. In Experiment 5, the film formation process employed
mono-silane to form a poly-crystalline silicon film. Specifically,
while the interior of the reaction tube 2 was set at 620.degree. C.
and 26.6 Pa (0.2 Torr), mono-silane set at 0.4 liters/min was
supplied, to form a poly-crystalline silicon film on semiconductor
wafers W.
FIG. 9 is a graph showing the relationship between the cumulative
film thickness on target substrates and the number of cracks on a
by-product film, where a film formation process using the
conditions of Experiment 5 to form a poly-crystalline silicon film
having a thickness of 0.5 .mu.m was repeated a plurality of times.
As shown in FIG. 9, where the cumulative film thickness was 6 .mu.m
or less, cracks were scarcely generated. On the other hand, where
the cumulative film thickness exceeded 6 .mu.m, a lot of cracks
were generated. From these results, it has been found that, where
mono-silane is used to form a poly-crystalline silicon film, the
threshold of the cumulative film thickness should be set at 6
.mu.m.
<Consequence and modification>
As described above, according to the embodiments described above, a
method for using a film formation apparatus for a semiconductor
process is arranged as follows. Specifically, at first, the process
conditions of a film formation process are determined to form a
thin film on a target substrate (semiconductor wafers W)
accommodated in a reaction chamber (reaction tube 2) of a film
formation apparatus (heat processing apparatus 1). The process
conditions include a preset film thickness of the thin film (for
example, a silicon nitride film or poly-crystalline silicon film)
to be formed on the target substrate. Then, the timing of
performing a cleaning process is determined, in accordance with the
process conditions, to remove a by-product film deposited on an
inner surface of the reaction chamber due to the film formation
process. The timing is defined by a threshold concerning a
cumulative film thickness that is a value obtained by multiplying
the number of repetitions of the film formation process by the
preset film thickness.
For example, it is assumed that the cumulative film thickness does
not exceed the threshold where the film formation process is
repeated N times (N is a positive integer and preferably 2 or
more), but exceeds the threshold where the film formation process
is repeated N+1 times. In this case, the first to Nth processes,
each consisting of the film formation process, are preformed
continuously without interposing the cleaning process therebetween.
Then, the cleaning process is performed after the Nth process and
before an (N+1)th process consisting of the film formation
process.
For this purpose, the control section (control section 100) of the
film formation apparatus recognizes the process conditions of the
film formation process selected by, e.g., an operator, and then
determines the timing of performing the cleaning process in
accordance with the process conditions. In this case, a specific
process recipe may be selected from a plurality of process recipes
prepared in advance, or a specific process recipe may be formed by
adding some values of the process conditions into a basic process
recipe. Then, under the control of the control section, the film
formation process and cleaning process are performed by the film
formation apparatus. Alternatively, the timing of performing the
cleaning process may be determined by an operator and input into
the control section.
The data necessary for determining the timing of performing the
cleaning process may be obtained by performing preliminary
experiments, such as those shown in Experiments 1 to 5 described
above. For example, the threshold of the cumulative film thickness
may be determined in accordance with the relationship between the
number of cracks generated on the by-product film and the
cumulative film thickness. Alternatively, the threshold of the
cumulative film thickness may be determined in accordance with the
relationship between the number of particles deposited on the thin
film and the cumulative film thickness.
Where the formed thin film is a silicon nitride film, the cleaning
gas may be a mixture gas of fluorine, hydrogen fluoride, and
nitrogen. On the other hand, where the formed thin film is a
poly-crystalline silicon, the cleaning gas is preferably a mixture
gas of fluorine and nitrogen. The cleaning gas can be any gas as
long as it can remove a by-product film deposited inside the
reaction chamber. For example, a gas containing fluorine and/or
chlorine, such as ClF.sub.3, may be used.
In the embodiment described above, the cleaning gas contains
nitrogen gas as a dilution gas. The dilution gas preferably
contains a dilution gas, because the process time can be more
easily controlled if the gas is so arranged. However, the cleaning
gas may contain no dilution gas. The dilution gas consists
preferably of an inactive gas, such as nitrogen gas, helium gas
(He), neon gas (Ne), or argon gas (Ar).
In the embodiments described above, the reaction tube 2, lid 6, and
wafer boat 11 are made of quartz. Alternatively, these members may
be made mainly of a material selected from other silicon-containing
materials, such as silicon carbide (SiC). Further, the lid 6 may be
made of, e.g., stainless steel. Where the reaction tube 2 is made
of a silicon-containing material, such as quartz, not only the
surface of by-product films is cracked, but also the surface of the
reaction tube may be cracked. Accordingly, in order to avoid ill
effects on the subsequent film formation process, it may be
preferable to perform the cleaning process frequently. In general,
one cleaning process is performed after the film formation process
is repeated two times or more (i.e., the number N described above
is 2 or more). However, there may be a case where a cleaning
process is performed every time the film formation process is
performed, depending on the process conditions of the film
formation process.
In the embodiments described above, the process gas feed lines 17
are disposed in accordance with the type of process steps.
Alternatively, for example, a plurality of process gas feed lines
17 may be disposed in accordance with the type of gases (e.g., five
lines for fluorine, hydrogen fluoride, DCS, ammonia, and nitrogen).
Further, a plurality of process gas feed lines 17 may be connected
to the sidewall of the reaction tube 2 near the bottom, to supply
each gas through a plurality of lines. In this case, a process gas
is supplied through the plurality of process gas feed lines 17 into
the reaction tube 2, and thereby more uniformly spreads in the
reaction tube 2.
In the embodiments described above, the heat processing apparatus
employed is a heat processing apparatus of the batch type having a
single-tube structure. However, for example, the present invention
may be applied to a vertical heat processing apparatus of the batch
type having a reaction tube of the double-tube type, which is
formed of inner and outer tubes. Alternatively, the present
invention may be applied to a heat processing apparatus of the
single-substrate type. The target substrate is not limited to a
semiconductor wafer W, and it may be a glass substrate for, e.g.,
an LCD.
The control section 100 of the heat processing apparatus is not
limited to a specific system, and it may be realized by an ordinary
computer system. For example, a program for executing the process
described above may be installed into a multi-purpose computer,
using a recording medium (a flexible disk, CD-ROM, or the like)
with the program stored therein, so as to prepare the control
section 100 for executing the process described above.
Means for supplying a program of this kind are diverse. For
example, a program may be supplied by a communication line,
communication network, or communication system, in place of a
predetermined recording medium, as described above. In this case,
for example, a program may be pasted on a bulletin board (BBS) on a
communication network, and then supplied through a network while
being superimposed on a carrier wave. The program thus provided
would then be activated and ran under the control of the OS of the
computer, as in the other application programs, thereby executing
the process.
Additional advantages and modifications will readily occur to those
skilled in the art. Therefore, the invention in its broader aspects
is not limited to the specific details and representative
embodiments shown and described herein. Accordingly, various
modifications may be made without departing from the spirit or
scope of the general inventive concept as defined by the appended
claims and their equivalents.
* * * * *